The use of transmission line or cable hangers, or clamps, configured to attach a transmission line or cable to a support, such as an antenna tower, have been known for many years. The advent of electronic equipment has caused a few problems related to coupling of a hugely increased number of transmission lines along antenna towers due to a limited space capable of accommodating these lines. Typically, since installation of cables is associated with safety considerations as well as with the time and expense involved with installing these lines, it is highly desirable to minimize both the amount of time and the complexity of the work required for coupling cables to support structures. To address these issues, various structures of cable hangers, designed to rapidly attach cables to support structures, have been recently developed.
A typical cable holder is illustrated in FIGS. 1 and 2 and includes inner and outer cable hangers 110 coupled to one another so that the outer hanger may be added later to accommodate additional cables without disassembling the previously installed hanger(s). Attachment of the inner hanger 110 to a support 118 as well as coupling the hangers to one another are realized by compressing opposite arms 112 so that locking fingers 114 are first inserted into an opening 116 and then, upon ceasing the compressing force, spread apart to reliably engage the rim of the opening. Support 118 may be horizontally or vertically disposed, and may include a plurality of openings to accommodate multiple hangers 110.
Insertion of the cable holder may pose several problems. For example, if the cable holder, as shown in FIGS. 1 and 2, is assembled before its attachment to the support 118, the access to the inner hanger may be limited because the outer hanger blocks the inner one, which is, thus, difficult to reach manually. Note that the inner and outer hangers may rotate relative to one about an axis of symmetry S′-S′ upon insertion of the locking fingers 114 into the opening 116. However, because this rotation occurs about the axis of symmetry common to both hangers, the outer hanger blocks the inner hanger regardless of the relative angular position of the hangers. Thus, this structure necessitates the use of instruments, which are a) inconvenient, since the direct access to the inner hanger is still blocked by the outer hanger, and b) undesirable, because having additional instruments on a tall tower imposes an additional physical and logistical hardship on the serviceman.
If, however, the cable holder of FIGS. 1 and 2 is deployed by initially attaching only the inner hanger with a respective cable to the support 118, further installation of the outer hanger in response to the increased demands for additional cables may be associated with difficulties caused by climatic conditions. Indeed, typically, cables are installed on tall towers. As a consequence, low temperatures and strong winds may critically complicate the attachment of the outer hanger to the inner one. Also, gradual installation of subsequent outer hangers may be associated with still another problem stemming from variations of the size of the opening 116 leading to unreliable securing the hangers to one another and to the support 118. Overall, the above-discussed problems may detrimentally affect the reliability of the installation as well as the safety of the worker.
Furthermore, the cable holder of FIGS. 1 and 2 is configured to lock a respective cable by compressing the arms of the hangers against this line upon inserting the locking fingers 114 into the opening 116. Yet, the inherent elasticity of the arms of the hanger may not be sufficient to prevent displacement of the cables along the tower for a variety of reasons. Even those hanger designs that have mechanisms for penetrating or biting into the cable jacket may not prevent longitudinal movement of the cable because the frictional coefficient between the metal hanger and the plastic cable jacket is very low. The polyethylene typically used for cable jackets is a soft material that has an inherent lubricant quality. In addition, the cable jacket can “cold flow” which reduces the holding force of the cable hanger over time, resulting in cable slippage.
It is therefore desirable to provide a stackable cable holder configured to provide an easy installment of cables as well as reliable securement thereof.